Stop writing new session data back to the legacy tasks.session_json
column; updateTaskSession now upserts the active task_sessions row
(updating the session pointed to by tasks.active_session_id, creating
one when absent), and getTaskSession reads from the same row so
session data has a single source of truth. Adds migration 27 to
backfill pre-existing tasks.session_json values into task_sessions
idempotently via INSERT OR IGNORE guarded on task_id. The legacy
column is kept for read-only history and is not dropped.
Stop silently swallowing duplicate-column errors in the migration
runner; any real migration failure now throws. Replace try/catch-based
column additions in ensureOptionalColumns and migrations 19-22 with
pragma table_info checks so repeated startup is idempotent without
tolerating error signals. Reorder initializeDatabase so runMigrations
runs before ensureOptionalColumns to avoid migration 13 adding columns
that ensureOptionalColumns already created on fresh databases.
ZacharyZhang-NY